Modern paper making production lines operate at very high speeds, and must be actively controlled to achieve acceptable uniformity. During production, it is important to maintain uniform cross-machine direction (CD) weight, moisture, and caliper profiles. In particular, non-uniform CD moisture profiles affect the final paper quality and converting operations by causing dimensional instability, curling and wrinkling of the paper sheet. A non-uniform CD moisture profile could also affect running performance of the paper machine by increasing the risk of sheet breaks. Modulation of the moisture profile can be achieved either by, for example, manipulating steam, water, or infrared energy output onto the sheet, with the latter being more prevalent with coated paper applications.
Modern paper making machines include control systems that control many components, including profiling devices. When actuated, these profiling devices can affect the CD moisture profile of the web by applying steam, water or infrared energy. Of course, the operation of profiling devices increases the manufacturing costs. In the case of water addition from rewet profilers, operating cost includes water purification, increased steam usage in the dryer section because the sheet must be over-dried before rewetting the sheet, reduced production because less steam is available in the dryer section, and seasonal availability or cost of water in some regions. In the case of steam addition from steam profilers, operating cost includes production of superheated steam. In the case of infrared energy output from infrared profilers, operating cost includes gas or electric usage for generating infrared energy. Thus, generally the greater the uniformity, the greater the use of the profiling devices and consequently, the greater the operating costs.
The efficient production of webs with quality profiles is further complicated when multiple CD profiling devices are employed to control the same profile measurement. This multiple profiling device arrangement is often employed to achieve maximum flexibility and responsiveness. However, multiple profiling devices may work against one other and cause more total expenditure of resources than is necessary.
There is therefore a need in the art for a method of controlling CD moisture that achieves greater efficiency while maintaining acceptable uniformity.